Until recently, the most advantageous method of fertilizing a tract of ground has been to broadcast fertilizers, both dry and liquid, over the ground and then disc or chisel them under the surface. Injecting fertilizers into the ground along desired bands, also known as "deep placement," has been gaining in popularity. As compared with broadcasting fertilizers, some advantages of injecting them are as follows:
(1) Phosphate which is applied to the soil becomes tied up by the presence of iron, aluminum, and calcium. By deep-placing fertilizer in a narrow band, the amount of phosphate so tied up is reduced.
(2) Since deep-placement requires substantially less tillage, exposure of topsoil to wind and erosion is reduced.
(3) The effect of knifing-in dry and liquid fertilizer to a depth (8 to 10 inches) below that of disc level (5 to 8 inches) is that soil below the normal fertilizer level is loosened, thereby further reducing the need for tillage.
(4) More water is available for a longer period of time in dry seasons, since it may reside at the lower levels created by deep-placement.
(5) Depleted nutrients, once abundant in the lower soil levels, are replenished.
(6) Soil compaction and operating costs are reduced, since large, dry fertilizer spreader trucks are eliminated.
A typical arrangement for deep-placing fertilizer is a series of hollow injector knives attached to a tool bar which is mounted to a three point hitch at the rear of a tractor, whereby the knives can be lowered into the ground. Towed behind the tool bar is a four-wheeled hopper containing some means for blowing dry fertilizer through tubing connected to the knives. Towed behind the hopper is a liquid fertilizer tank which includes pump and hose connections for delivering fertilizer through hoses connected anterially to each knife.
Although, in general, this arrangement has performed satisfactorily, there are problems related to its having two articulated elements spaced away from the tractor by the tool bar. Maneuverability is limited, and reversing directions at the end of each swath is difficult and requires a great deal of unused margin land. It is also time-consuming and difficult to align and connect the second of the two articulated elements.